Arc welding apparatus



June 15, 1937. E. THIEMER 2,084,168

ARC WELDING APPARATUS Filed May 29, 1936 lr'vvencori Erwin Thiem r", byW a. dwiq is Attorney.

Patented June 15, I 1931 FFIE ARC WELDING ArrARATUs Erwin Thiemer,Hennigsdorf; Germany, assignor to General Electric C New York ompany, acorporation oi? Application May 29, 1936, Serial No, 82,586

' In Germany June 8, 1935 4 Claims.

My invention relates to arc welding apparatus for automaticallyfeedingshort length electrodes.

In order to improve the arcing characteristics of electrodes, as well asthe qualitiesof the metals deposited thereby, heavy -flux coatings arefrequently applied to the electrodes. These electrodes are commonlysupplied in short lengths having one end bareol of flux for connectionto one terminal of a source of welding current.

When such an electrode has an appreciable length, say from 18 to 24inches, and when relatively high welding currents are employed, there isof necessity an appreciable voltage drop between the two ends of theelectrode, This drop changes as the electrode is consumed. When the arcis first struck the. resistance of the electrode increases quite rapidlydue to the temperature rise caused by thecurrent flowing through theelectrode. During welding the resistance of the electrode consequentlyreaches a maximum value and then begins to decrease as the electrode isconsumed and becomes shorter. I

In automatic arc welding machines adapted for feeding short lengthelectrodes the voltage re spon'sive device used for controlling the feedof the electrode is connected across the electrode and the aremaintained at its arcing terminal,

and the variation in voltage drop in the electrode which changes withthe length or the electrode materially affects the arc voltagemaintained by the feeding means under the control of the voltageresponsive device. Because of the drop in voltage in the electrode, theai'c voltage is a minimum when the welding operation is started with anew electrode; increases for a short time, and

then gradually decreases with the consumption of the electrode. Thevoltage responsive device of such machines does not, consequently,maintain an arc of substantially uniform voltage during a weldingoperation.

It is an object oi my invention to provide means for compensating forthe changes in voltage drop in short length electrodes fed by auto-'matic arc welding machines so that the voltage responsive devices ofsuch machines are enabled to control the feed of the electrodes in amanner to maintain a substantially uniform arc voltage during welding.

My invention will be better understood from a consideration of the twoembodiments thereoi diagrammatically illustrated in Figs. 1 and 2 of thedrawing.

In Fig. 1, one end of'an electrode Hi is clamped in an electrode holderH having a feed rod l2 welded l5.

(Cl. Elli -8) which extends between and is engaged by feed rolls l3. Anare it is maintained between the other end of the electrode Hi and thework to be Current is supplied to the are N through the followingcircuit; from a source of welding current through conductor ifi work l5,are [4, electrode iii, feed rod l2, contact I"I,resistance l8, andconductor l9 back to the source of Welding current; A voltage responsivedevice 26; has its operating coil 2! connected across thearc i l, theelectrode "Land resistance l8. In the arrangement illustrated thevoltage respon sive device has been illustrated as a contact makingvoltmeter which by controlling circuits through conductors 22 controlsthe speed and direction of rotation of the feed rolls iii. The voltmetermay form a part of any suitable control. It may be part of a system suchas shown in United States Letters Patent 1,541,582; Wilbur L. Merrill,granted June 9, 1925. With such a control the feed rolls 13 are rotatedthrough a reduction gearing 23 and a transmission involving a disc 24and rolls 25 and 26 by a'ieed motor 2'] connected to a source of supplywhich through conductors 22 and the contacts of voltmeter Zll energizescoils 28 and as to control the engagement of these rolls 25 and 26 withdisc 2E and thus the direction and rate of feed of the electrodeby'teecl rolls l3.

It will be noted that as the electrode H) is consumed in the are H, thecontact I! attached to feed rod 12 will move along the resistance Itvarying the amount of this resistance in circuit with the electrode. Inthe arrangement shown the amount oi resistance is decreased from a smallamountto zero, totake care of the initial increase in resistance of theelectrode due to heating and is thereafter increased to compensate forthe decreasing resistance of the electrode Iii, which during the weldingoperation is becoming shorter and shorter. The total voltage drop,however, across the resistance i8 and electrode i0 is substantiallyconstant, and since the voltage responsive device is connected acrossresistance l8, electrode ill and are H and acts to maintain their totalvoltage drop substantially constant, the voltage drop across the arc 54will resistance per unit length of the electrode I0.

Current is supplied to the electrode to through coated electrodesalthough it a contact 3| which engages the feed rod 30. As in Fig. 1,the electrode [0 and feed rod 30 are fed relatively to the contact :3!by feed rolls I3, the speed and direction of which are controlled by thevoltage responsive device 20. As the electrode I0 is consumed and thevoltage drop across it becomes less and less, more and more of the feedrod 30 is placed in circuit with the electrode and the increased voltagedrop in the feed rod 30 compensates for the decreased voltage drop inthe electrode 10. With this arrangement the voltage responsive deviceconnected across the are N, electrode l0 and feed rod 30 operates tomaintain a substantially uniform voltage across the arc, since the totalvoltage drop through the electrode in and feed rod 30 is substantiallyconstant.

As has been noted above, because of the heating of the electrode and itsincrease in resistance due to this factor, the resistance of theelectrode does not at first decrease in exact correspondence with itsconsumption during welding and if the resistance changes due to thisheat ing effect is material, it may be neutralized by properlyproportioning the cross section of the feed rod 30 or by making it ofmaterials of different electrical conductivity so that a completecompensation for changes in voltage drop in the electrode may befurnished by a proper decrease and increase in voltage drop in the feedrod 30 as the welding operation progresses and the electrode isconsumed.

My invention is not limited in its application to automatic machinesused for feeding heavily is expected to be of greatest utility for thispurpose. It may be used for feeding bare or lightly coated electrodes toimprove the voltage regulation of the welding are and thus the quality'of the weld metal deposited. Furthermore the entire electrode is notnecessarily included in the welding circuit, for my invention is equallyeffective for feeding electrodes to which the welding current issupplied through a length thereof by contact means attached to theelectrode at a substantial distance from its arcing terminal.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Are welding apparatus comprising means for supplying welding currentthrough the full length of a, welding electrode to an are at its arcingterminal, means in series circuit with said electrode for compensatingfor the change in voltage drop in said electrode with its consumptionduring welding, a voltage responsive device connected across said arc,said electrode and said compensating means, and means controlled by saidvoltage responsive device for feeding said electrode and for operatingsaid compensating means.

2. Arc Welding apparatus comprising a welding circuit, a resistanceconnected in said welding circuit in series with that portion of anelectrode consumed during welding, a voltage responsive device connectedacross said resistance, said electrode, and the are maintained at thearcing terminal of said electrode, means under the control of saidvoltage responsive device for feeding said electrode to compensate forits consumption during welding, and means for varying said resistance inresponse to the movement of said electrode to produce during welding asubstantially uniform voltage drop across said resistance and theunconsumed portion of said electrode.

3. Are welding apparatus comprising a resistance connected in serieswith that portion of an electrode consumed during welding, means forsupplying welding current through said resistance and said electrode toits arcing terminal, a contact making voltmeter connected across saidresistance, said electrode, and the are maintained at the arcingterminal of said electrode, means including said voltmeter for feedingsaid electrode toward the work to compensate for its consumption in thearc, and means responsive to the movement of said electrode for varyingsaid resistance and for producing during welding a substantially uniformtotal voltage drop across said resistance and said electrode.

4. Are welding apparatus comprising an electrode holder having anextended conductive por tion the resistance per unit length of which issubstantially the same as the resistance per unit length of an electrodeone end of which is supported in said holder, means for supplyingwelding current to said electrode through said conductive portion ofsaid holder, means for feeding said electrode and said conductiveportion of said holder relative to said current supplying means towardthe work to be welded to compensate for the consumption of saidelectrode during welding, and means including a voltage responsivedevice the terminals of which are connected to said current supplyingmeans and to said work, for controlling said feeding means.

ERWIN THIEMER.

